结合JavaGuideIO部分内容食用更佳

在Java中，I/O（输入/输出）操作主要有三种模型：BIO（Blocking I/O，阻塞I/O）、NIO（Non-blocking I/O，非阻塞I/O）和AIO（Asynchronous I/O，异步I/O）。这三种模型在处理I/O操作时的工作方式和适用场景各不相同。下面对它们进行详细介绍：

// 服务器端
ServerSocket serverSocket = new ServerSocket(8080);
while (true) {
    Socket clientSocket = serverSocket.accept(); // 阻塞等待连接
    new Thread(() -> {
        try {
            BufferedReader in = new BufferedReader(
            	new InputStreamReader(clientSocket.getInputStream())
            	);
            String message = in.readLine();
            System.out.println("Received: " + message);
            clientSocket.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }).start();
}

// 客户端
Socket socket = new Socket("localhost", 8080);
PrintWriter out = new PrintWriter(socket.getOutputStream(), true);
out.println("Hello, Server!");
socket.close();

import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.*;

public class NioServer {
    public static void main(String[] args) throws IOException {
        // 打开ServerSocketChannel
        ServerSocketChannel serverChannel = ServerSocketChannel.open();
        serverChannel.configureBlocking(false);
        serverChannel.socket().bind(new InetSocketAddress(8080));

        // 打开Selector
        Selector selector = Selector.open();
        serverChannel.register(selector, SelectionKey.OP_ACCEPT);

        ByteBuffer buffer = ByteBuffer.allocate(256);

        while (true) {
            selector.select(); // 阻塞直到有事件
            for (SelectionKey key : selector.selectedKeys()) {
                if (key.isAcceptable()) {
                    // 接受连接
                    ServerSocketChannel srvChannel = (ServerSocketChannel) key.channel();
                    SocketChannel client = srvChannel.accept();
                    client.configureBlocking(false);
                    client.register(selector, SelectionKey.OP_READ);
                } else if (key.isReadable()) {
                    // 读取数据
                    SocketChannel client = (SocketChannel) key.channel();
                    buffer.clear();
                    int bytesRead = client.read(buffer);
                    if (bytesRead == -1) {
                        client.close();
                    } else {
                        buffer.flip();
                        byte[] data = new byte[buffer.limit()];
                        buffer.get(data);
                        System.out.println("Received: " + new String(data));
                    }
                }
            }
            selector.selectedKeys().clear();
        }
    }
}

import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.AsynchronousServerSocketChannel;
import java.nio.channels.AsynchronousSocketChannel;
import java.nio.channels.CompletionHandler;
import java.util.concurrent.Future;

public class AioServer {
    public static void main(String[] args) throws IOException {
        final AsynchronousServerSocketChannel serverChannel =
                AsynchronousServerSocketChannel.open().bind(new InetSocketAddress(8080));

        serverChannel.accept(null, new CompletionHandler<AsynchronousSocketChannel, Void>() {
            @Override
            public void completed(AsynchronousSocketChannel client, Void attachment) {
                // 继续接受下一个连接
                serverChannel.accept(null, this);

                // 处理当前连接
                ByteBuffer buffer = ByteBuffer.allocate(1024);
                client.read(buffer, buffer, new CompletionHandler<Integer, ByteBuffer>() {
                    @Override
                    public void completed(Integer bytesRead, ByteBuffer buf) {
                        if (bytesRead == -1) {
                            try {
                                client.close();
                            } catch (IOException e) {
                                e.printStackTrace();
                            }
                            return;
                        }
                        buf.flip();
                        byte[] data = new byte[buf.limit()];
                        buf.get(data);
                        System.out.println("Received: " + new String(data));
                        buf.clear();
                        client.read(buf, buf, this);
                    }

                    @Override
                    public void failed(Throwable exc, ByteBuffer buf) {
                        try {
                            client.close();
                        } catch (IOException e) {
                            e.printStackTrace();
                        }
                    }
                });
            }

            @Override
            public void failed(Throwable exc, Void attachment) {
                System.err.println("Failed to accept a connection.");
                exc.printStackTrace();
            }
        });

        // 阻止主线程退出
        try {
            Thread.currentThread().join();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}